Date Added: Jul 2011
In Orthogonal Frequency Division Multiple Access (OFDMA) systems, the delay of packets has a great impact on Quality of Service (QoS), especially for real-time transmission. The basic concept of resource allocation in an OFDMA system is to allocate a subcarrier to the user with the best channel condition in that subcarrier. However, when a retransmission technique is used, the packet delay of successfully transmitting failed packets may be quite large in conventional retransmission schemes. In this paper, the packet combining technique in the downlink OFDMA system is introduced in conjunction with frequency diversity to enhance the reliability of retransmissions and thus reduce the large time delay caused by retransmissions.